BOLL WEEVIL CONTROL BY USE OF POISON. 15 



formed. This usually means that the plant has reached the limit 

 of its ability to mature fruit. Naturally there is no advantage in 

 attempting to protect these forms, and poisoning during this period, 

 if conducted after the retained bolls are sufficiently large to escape 

 weevil injury, is bound to be profitless. The time when this con- 

 dition is reached varies widely with the season as well as with the 

 soil fertility, and these factors must always be taken into considera- 

 tion .in deciding whether additional poisoning is justified. 



EFFECT OF RAIN ON AN APPLICATION OF POISON. 



The effect of rain upon the application of calcium arsenate is a 

 subject of much importance. Experience has shown that a certain 

 amount of rainfall is desirable during the poisoning operations as 

 it induces the formation of dew, makes conditions more nearly ideal 

 for dusting, and apparently increases the amount of mortality se- 

 cured from the applications. Poisoning operations have been con- 

 ducted during periods of extreme drought when there was almost 

 no dew formation, but under such conditions it has been very difficult 

 to secure a thorough degree of control. On the other hand, ex- 

 cessive rain is detrimental, owing to the difficulty of getting the 

 poison to stay on the plants long enough to control the weevils. 

 This was especially true during some of the work in the extreme 

 southern districts in 1919. The rains encountered in this work 

 were excessive and in many cases occurred almost daily. Under 

 such conditions weevil poisoning can easily become an absolute im- 

 possibility but, as far as that is concerned, such conditions make it 

 practically impossible to raise cotton at all. 



It has been found that when an application is made under unfavor- 

 able conditions and the plants are dry, even a slight shower occurring 

 a short time later will wash off practically all the dust, while if con- 

 ditions during the application are more favorable for a large quan- 

 tity of the poison to adhere to the plants, a much heavier rain will 

 not interfere seriously with the effect of the treatment. As a gen- 

 eral rule it seems advisable to repeat an application immediately if 

 a drenching rain falls within 21 hours after treatment. Until more 

 information is secured on the subject, it undoubtedly will be best to 

 follow some such rule as this, but the question of degree of weevil 

 infestation and the conditions under which the application has been 

 made should undoubtedly be considered in connection with the ques- 

 tion of whether the application should be repeated. 



STARTING POISONING IN THE PRESENCE OF A COMPLETE INFESTATION. 



Many farmers make no move toward weevil poisoning until the 

 crop is seriously infested and in fact almost totally destroyed by the 



